This invention relates to a cylindrical plain bearing for rotatably supporting a rotating shaft.
A plain bearing for rotatably supporting a rotating shaft is formed to a cylindlical shape so as to be fitted on the inner surface of a housing. Frictional wear and seizure of this plain bearing are suppressed by the lubricating effect and cooling effect of the lubricating oil, which are supplied into a clearance between the inner surface of this plain bearing and the rotating shaft, and the noise suppressing effect can also be brought about by the buffer or damper action of the lubricating oil. As the thickness of an oil film to be formed between the inner surface of the plain bearing and the rotating shaft becomes thicker, that is to say, as the amount of the lubricating oil further increases, the above-mentioned suppressing effect produces good results.
In order to increase the amount of the lubricating oil to be retained, it had been made to provide a plain bearing having a number of fine grooves which are circumferentially formed on the inner surface of the bearing, the fine grooves being parallel with one another and being arranged to extend at intervals in the axial direction of the bearing, the inner surface comprising the fine grooves and lands which are defined as portions of the bearing left between the fine grooves, the fine grooves and the lands being arranged at intervals in the axial direction of the bearing, the fine grooves having a depth of several micro meters (.mu.m).
JP-A-59-73620 discloses a plain bearing having a number of fine grooves which are circumferentially formed on the whole inner surface of the bearing, the fine grooves being arranged at intervals in the axial direction of the bearing and being inclined at an angle of 0 to about 5 degrees relative to the circumferential direction of the bearing. This arrangement allows a large amount of lubricating oil to be supplied into the fine grooves, thereby promoting the heat dissipation (Prior Art 1).
JP-U-63-62621 discloses a plain bearing having fine grooves which are circumferentially formed on the inner surface of the bearing, the fine grooves being arranged to extend at intervals in the axial direction of the bearing, the fine grooves in the vicinity of both ends of bearing metals being arranged in a deeper depth than those of the axial central portion of the bearing metals so that a large amount of lubricating oil can be retained in the vicinity of the both ends. With this arrangement, the amount of the lubricating oil is increased in the vicinity of the both ends, where the bearing is subjected to a high shock loading caused by a partial contact of a rotating shaft, thereby suppressing the heat generation in the both ends of the bearing (Prior Art 2).
JP-U-63-53922 discloses a plain bearing having a number of fine grooves which are circumferentially formed on the surface of the bearing, the fine grooves being arranged to extend at intervals in the axial direction of the plain bearing, thereby having a large proportion of sliding surface area which is obtained by making the fine grooves in the vicinity of both ends of bearing metals in a larger pitch than those of the axial central portion of the bearing metals. With this arrangement, the lowering in the durability of the bearing is intended to be suppressed by reducing the number of the fine grooves in the vicinity of the both ends of the bearing metals, where the rotating shaft is in partial contact with the bearing metals, thereby preventing the decrease in the area which is subjected to the axial loading due to the formation of the fine grooves, as much as possible, so as to reduce the specific load (Prior Art 3).
In these Prior Arts 1 to 3, every plain bearing has a number of fine grooves which are circumferentially formed on the inner surface of the bearing, the fine grooves being arranged to extend at intervals in the axial direction of the bearing, the inner surface having continuous fine grooves and lands the latter of which are defined as portions of the bearing left between the fine grooves. Each of the lands may offer a resistance when the lubricating oil outflowing in the axial direction of the bearing, to thereby prevent an inflow pressure from dropping when the lubricating oil flowing into a clearance between the inner surface and the rotating shaft and also allow a large amount of lubricating oil to flow through the fine grooves so as to promote the heat dissipation.
However, in these Prior Arts, because every plain bearing is configured to have the same height lands which are obtained by forming the fine grooves, the lands did not sufficiently function as the resistance when the lubricating oil outflowing in the axial direction of the bearing, or the conformability between the rotating shaft, the lands and the fine grooves recesses was not sufficient in use.